As the by-product of wastewater treatment, a large amount of sludge is generated annually. Turning this waste into a resource is a feasible and sustainable strategy to reduce potential environmental risks and recover energy. As a way to realize the international goal of carbon dioxide emission peak and carbon neutrality, producing biochar from sludge has gained worldwide attention. This review evaluates recent progress in synthesis techniques for biochar of sludge origin. Different preparation techniques and their key affecting factors are compared and described. The obtained sludge-derived biochar could be employed for eliminating aqueous pollution or purifying wastewater, mainly through adsorption and catalytic reactions. The removal of various pollutants by sludge-derived biochar and its related mechanisms are discussed and summarized in detail. This review will be conducive for a comprehensive understanding of recent progress in sludge-derived biochar study and for guiding the purposeful production of biochar, as well as for developing wastewater purification technology based on sludge-derived biochar.

To address the challenges of combustion stability and pollutant control during biomass co-combustion in coal-fired boilers under deep peak regulation, a numerical simulation study was conducted on a 660 MW front-and-rear wall opposed-fired pulverized coal boiler using computational fluid dynamics (CFD) technology. First, the reliability of the numerical model was validated under the Boiler Maximum Continuous Rating (BMCR) condition by comparing the simulated results of furnace outlet temperature and NO concentration with on-site operational data, with relative errors of 1.2% and 1.9%, respectively, both within the acceptable range of 5%. Subsequently, the effects of different biomass co-combustion ratios (0%, 5%, 10%, 15%, 20%) and injection positions (primary air nozzles of lower, middle, and upper burners) on the in-furnace velocity field, temperature field, component distribution (O₂, CO, CO₂), and NO emissions were systematically analyzed. The results indicate that increasing the biomass co-combustion ratio does not alter the overall variation trend of flue gas components but significantly affects their concentrations: the O₂ content at the furnace outlet decreases gradually, while the CO₂ content increases, and the NO emission concentration decreases continuously. A 20% co-combustion ratio is identified as the optimal choice, balancing combustion efficiency and NO reduction. Regarding injection positions, biomass injected at the middle burner’s primary air nozzle achieves the best NO control effect, reducing NO emissions by 22% compared to pure coal combustion. This is attributed to the formation of a stable reducing atmosphere in the main combustion zone, which facilitates NO_x reduction. The research findings provide valuable theoretical references and technical support for the parameter optimization and safe, low-emission operation of biomass co-combustion in large-scale coal-fired boilers.

To address the issue of coarse fly ash particles resulting from co-firing inferior coal in utility boilers—which impairs resource utilization and economic performance of power plants—this study conducts laboratory-scale investigations on coal combustion characteristics and fly ash particle size distribution, alongside field tests on coal blending and combustion optimization for a 330 MW unit. The research is approached from the perspective of reducing technical costs while avoiding large-scale equipment modifications. The formation mechanism of large fly ash particles is systematically analyzed, and optimization strategies are proposed. Laboratory results demonstrate that the proportion of coarse fly ash particles exhibits significant correlations with sulfur and pyrite content in coal, fuel ignition temperature, combustion burnout difficulty, and slagging propensity. Higher sulfur content, elevated ignition temperatures (> 680 °C), and lower burnout rates correspond to increased proportions of particles larger than 45 μm (reaching up to 38.5%). The fundamental mechanism involves the adhesion of molten (Fe–O–S) eutectics—formed through the oxidation of iron and sulfur—to other particles, thereby generating larger agglomerates. Field tests indicate that by increasing the as-fired coal calorific value to 4191 kcal/kg, reducing sulfur content to 1.04%, decreasing the proportion of low-reactivity coal, and optimizing combustion parameters (oxygen concentration at 3.8%, reduced primary air flow, and appropriately increased over-fire air opening), the proportion of fly ash particles exceeding 45 μm decreased from 52.2% to 36.0%, meeting the utilization standard for Grade III fly ash. This research achieves the technical objective of reducing coarse fly ash proportions through optimization measures without equipment modification, providing an economically viable solution for the resource utilization of fly ash from utility boilers.